[Xen-users] massive packet loss under network and disk load

[Steve Wray <steve.wray@xxxxxxxxx>]

As mentioned on a post to a thread about drbd and Xen I've been seeing 
some horrific packet loss under network and disk IO load which has been 
causing huge problems for drbd syncing and replication.
After testing many parameters and settings I have found that this 
appears to make the problem go away:
vif = [
        'rate=20MB/s,mac=AA:01:06:6D:FD:02, bridge=xenbr2'
 ]

'this' being the 'rate=20MB/s'.

I'm not sure if this is merely brushing the problem under the carpet 
but, all other things being at default settings, adding and removing the 
rate option from the vif reliably makes the problem go away or come back.
The thing that worries me is that even with this parameter on the vif I 
still see what I'd call massive packet loss on the vif for this domU as 
seen in xm top.
All the dropped packets are RX

It looks like this:

Net0 RX: 544045974bytes  6253667pkts        0err    52645drop  TX: 
334397858bytes  3644125pkts
I hope that I am interpreting this correctly, that the '52645drop' 
indicates RX packets dropped...
I am seeing hundreds of drops per second.

Within the domU, ifconfig shows no dropped packets or errors.

On dom0, ifconfig shows TX packets dropped:

vif2.0    Link encap:Ethernet  HWaddr FE:FF:FF:FF:FF:FF
          inet6 addr: fe80::fcff:ffff:feff:ffff/64 Scope:Link
          UP BROADCAST RUNNING NOARP  MTU:1500  Metric:1
          RX packets:4187429 errors:0 dropped:0 overruns:0 frame:0
          TX packets:7189734 errors:0 dropped:60679 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:383941238 (366.1 MiB)  TX bytes:1911795684 (1.7 GiB)



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